The outcome of a meeting last week among four Southeast Asian countries could determine whether construction of the first of 11 controversial dams on the Mekong River can proceed.

The dams are designed to generate electricity for the region, but environmentalists fear they will disrupt the Mekong's delicate freshwater ecology, which supports dozens of other critical species, and that they will threaten local communities who rely on the river for food and jobs.

This giant fish, found near the Cambodia-Vietnam border in 2002 by National Geographic Emerging Explorer Zeb Hogan, measured 162 inches (413 centimeters) from nose to tail.

Mekong Giant Catfish

Biologists have warned that the Xayaburi Dam proposed for the main stem of the Mekong River in Laos will block the migratory routes of dozens of fish species and could place 41 fish species at risk of extinction, including the critically endangered Mekong giant catfish.

Damming the Mekong

Photograph by Eugene Hoshiko, AP

The Dachaoshan dam in Yunnan province, China is one of many dams on the approximately 3,000-mile (4,800-kilometer) Mekong River.

The river is traditionally separated into two parts on maps: The upper Mekong flows through China, where it is known as the Lancang River, while the lower Mekong runs alongside Myanmar and through Laos, Thailand, Cambodia, and Vietnam before emptying into the South China Sea.

The newly proposed Xayaburi Dam in northern Laos is the first of 11 proposed dams planned for construction on the lower Mekong River. Nine dams are planned for Laos, and two others are slated for Cambodia.

The Xayaburi Dam will take eight years to complete and cost an estimated $3.5 billion. It will generate 1,260 megawatts of electricity, most of which will be sold to Thailand.

Published March 30, 2011

Mekong Giant Catfish Release

In terms of biodiversity, the Mekong River is second only to the Amazon among the world's great rivers. As a home to more than 1,000 fish species, the Mekong supports the world's largest freshwater fishery, and it provides food and income—through fishing, farming, ecotourism, and other jobs—for many of the 65 million people who live in the Lower Mekong basin.

The Mekong is unique among the world’s large rivers because "the fish diversity is extremely high, the diversity of migratory species is extremely high, and human dependence upon these species for fisheries is extremely high," said Peter McIntyre, a freshwater conservation expert at the University of Wisconsin-Madison.

"You put all of that together, and putting a large dam in the Mekong is likely to cause major problems."

Giant Carp

Cambodian fishermen pose with a giant carp caught on the Tonle Sap River in 2003.

The builders of the Xayaburi Dam have promised to create "fish passages" that would allow fish to continue their migrations.

But International River's Ame Trandem said no fishery technology currently exists that can guarantee safe passage for the Mekong's numerous fish species.

"Right now, all the evidence points to the fact that fish passages will not work on the Mekong River because you're dealing with such a high volume of fish and such a large number of fish species," Trandem said.

Mekong Giant Catfish

Photograph by Sukree Sukplang, Reuters

A Thai fishery department official catches a 66-pound (33 kilogram) Mekong giant catfish in 2006. The fish’s eggs were harvested as part of a captive breeding program and effort to restore giant catfish populations in the Mekong River system.